Changed water pump flushed radiator
changed head gasket but oil and water is
still mixing even some coming up in one of
the spark plug
Sounds like there is a crack somewhere, was the head checked for cracks when it was off?
The repair man said he had pressure test it so I just don't know what to do now
If you have coolant coming into a cylinder then he is full of shxt. A pressure test would most definitely verified a leak. Your situation is not good, either the repair was done wrong or there is a crack somewhere.
Looking for a Used Cube in your area?
CarGurus has 24 nationwide Cube listings starting at $2,950.
Search Nissan Cube Questions
Nissan Cube Experts